RFR: Disable biased locking by default

[Roman Kennke]

Am 05.09.2017 um 19:44 schrieb Aleksey Shipilev:
> Hi,
>
> I think it makes sense to disable biased locking by default:
>
> $ hg diff
> diff -r d64a5a4a4366 src/share/vm/runtime/arguments.cpp
> --- a/src/share/vm/runtime/arguments.cpp	Mon Sep 04 22:35:03 2017 +0200
> +++ b/src/share/vm/runtime/arguments.cpp	Tue Sep 05 19:43:21 2017 +0200
> @@ -2075,6 +2075,14 @@
>      }
>      FLAG_SET_DEFAULT(ShenandoahUncommitDelay, max_uintx);
>    }
> +
> +  // Current Hotspot machinery for biased locking may introduce lots of latency hiccups
> +  // that negate the benefits of low-latency GC. The throughput improvements granted by
> +  // biased locking on modern hardware are not covering the latency problems induced by
> +  // it. Therefore, unless user really wants it, disable biased locking.
> +  if (FLAG_IS_DEFAULT(UseBiasedLocking)) {
> +    FLAG_SET_DEFAULT(UseBiasedLocking, false);
> +  }
>  }
>
>  void Arguments::set_gc_specific_flags() {
>
>
> Testing: hotspot_gc_shenandoah
>
> Thanks,
> -Aleksey
>
>
Ok with me. We need to document this in our wiki.

Roman